[ThinLTO][Cache] When remote caching is enabled, use the passed-in thin-LTO cache as temp directory

This ensures that we can move cached artifacts from the remote service to the temp directory because they
should be on the same disk volume.

rdar://126211886

Author: akyrtzi

llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h

@@ -244,6 +244,12 @@ class ThinLTOCodeGenerator {
   /// the processing.
   void setSaveTempsDir(std::string Path) { SaveTempsDir = std::move(Path); }
 
+  /// Set the path to a directory where to save temporaries from the remote
+  /// service.
+  void setRemoteServiceTempsDir(std::string Path) {
+    RemoteServiceTempsDir = std::move(Path);
+  }
+
   /// Set the path to a directory where to save generated object files. This
   /// path can be used by a linker to request on-disk files instead of in-memory
   /// buffers. When set, results are available through getProducedBinaryFiles()
@@ -385,6 +391,9 @@ class ThinLTOCodeGenerator {
   /// Path to a directory to save the temporary bitcode files.
   std::string SaveTempsDir;
 
+  /// Path to a directory to save the temporary remote service files.
+  std::string RemoteServiceTempsDir;
+
   /// Path to a directory to save the generated object files.
   std::string SavedObjectsDirectoryPath;
 

llvm/lib/LTO/ThinLTOCodeGenerator.cpp

@@ -1582,6 +1582,8 @@ void ThinLTOCodeGenerator::run() {
   // First, we need to remember whether the caller requests buffer API or file
   // API based on if the SavedObjectsDirectoryPath was set or not.
   bool UseBufferAPI = SavedObjectsDirectoryPath.empty();
+  if (SavedObjectsDirectoryPath.empty())
+    SavedObjectsDirectoryPath = RemoteServiceTempsDir;
   std::string TempDirectory;
   if (CacheOptions.Type == CachingOptions::CacheType::RemoteService &&
       SavedObjectsDirectoryPath.empty()) {

llvm/tools/lto/lto.cpp

@@ -619,6 +619,10 @@ void thinlto_codegen_set_cpu(thinlto_code_gen_t cg, const char *cpu) {
 
 void thinlto_codegen_set_cache_dir(thinlto_code_gen_t cg,
                                    const char *cache_dir) {
+  if (sys::Process::GetEnv("LLVM_THINLTO_USE_REMOTE_CACHE")) {
+    unwrap(cg)->setRemoteServiceTempsDir(cache_dir);
+    return;
+  }
   // FIXME: need to return error somehow.
   Error Err = unwrap(cg)->setCacheDir(cache_dir);
   if (Err)